Holsters are generally designed to offer protection to the handgun, secure its retention, and provide ready access to it. The need for ready access is often at odds with the need for security and protection, so the user must consider the individual's needs. Choosing the right balance can be very important, especially in the case of a defensive weapon holster, where failure to access the weapon quickly or damage or loss of the weapon due to insufficient retention or protection could result in serious injury or death to the user.

Holsters are generally designed to be used with one hand, allowing the handgun to be removed and/or replaced with the same hand. To be able to return the handgun to its holster one-handed, the holster must be made from stiff material that holds its shape so that the holster won't collapse when the object is no longer inside to give it support.

Holsters are generally attached to a person's belt or waistband or clipped to another article of clothing. Some holsters, such as ankle holsters, have integrated support. Other holsters may fit inside a pocket, to add stability and protection to the handgun, keeping it more reliably secure and accessible than if it were in the pocket alone.

Holsters are generally worn in a location where they can be readily accessible. Common locations are: at the waist (outside (OWB) or inside (IWB) the waistband), behind the back (small of back (SOB)), at the ankle, at the chest (in an elastic belly band or shoulder holster), or on the upper thigh. Holsters are sometimes contained in an external bag, such as a purse or fanny pack.

Since holsters are typically made from fairly stiff yet tough materials, there are a limited number of common choices. The traditional material, particularly for handgun holsters, is leather. It has an attractive appearance and can be dyed in many colors and/or embossed with elaborate designs for cosmetic reasons.

Ballistic nylon is another common fabric for holsters, as it is stiff, wear resistant, and thick enough to provide protection.

Molded plastics, such as Kydex, are also popular, due to their low cost and robustness.

Holster designs for firearms cover a wide range of shapes, materials, and retention/release mechanisms, from simple leather pouches hanging from a belt to highly protective holsters with flaps that cover the entire handgun, to highly adjustable competition holsters that hold the handgun at a precise position and release instantly when activated. The wide range of types indicates the highly varied circumstances in which holsters are used, and the varying preferences of the users.

Holsters can be divided into four broad categories by use: duty holsters, worn by uniformed peace officers and security personnel; tactical holsters, worn by military, security, and law enforcement personnel in certain situations; concealment holsters, worn by plainclothes peace officers and private persons; and sporting holsters, worn for shooting sports and hunting.

Duty holsters are designed to be carried openly, so concealment is not an issue, but retention and appearance are. Duty holsters can be made of leather (plain, basketweave, or glossy), nylon, or plastic; they are designed to be attached to a duty belt, and worn on the dominant side. Duty holsters are generally only found for service and compact size handguns as opposed to small subcompact handguns as these are generally only used for concealed carry.

The primary characteristic that often distinguishes duty holsters from all other holster designs is retention. Modern law enforcement duty holsters are available with varying levels of retention security (i.e. Level I, Level II, Level II+, Level III, etc.;[1] some security features are passive (such as retention screws, decoy straps, or hood guards), while others are active and require deliberate manipulation by the officer during the draw (such as traditional thumbreak snaps). While a higher level of retention will make it more difficult for a suspect to snatch a holstered handgun away from an officer, it may also reduce the speed and ease with which an officer may draw his handgun (especially if the security features are active and not passive). Therefore, when selecting a duty holster, an officer may be forced to find a compromise of speed and retention that he/she is comfortable with.

Tactical/military holsters are usually made of nylon or plastic. They may be made in a camouflage pattern to match the wearer's uniform. They are often of a drop-leg design and offer a retention device. Some military holsters still use the old flap design (also referred to as a "suicide" or "widow maker" holster, which is cumbersome and slow on the draw, but provides greater protection for the holstered firearm against the elements.[2]

There is some overlap between duty holsters, tactical holsters, and military holsters. Weapon retention is generally not as important a consideration in military use as it is in law enforcement due to the differences in their work environments.

Concealment holsters are designed to be easily concealed, as well as lightweight and unobtrusive. They are generally designed for subcompact and compact handguns since they are easier to conceal. Concealment holsters are designed to be worn under clothing, such as on the belt under a coat, under pants in an ankle holster, or in a trouser pocket. Since the holster is held close to the body, comfort is important, and concealment holsters often have broad surfaces in contact with the user's body, to distribute the pressure across a wider area and prevent abrasion of the skin. Protecting the handgun from the user's perspiration is often an important consideration in such carry locations. Often the outside of the holster is broader, to help break up the outline of the handgun and prevent printing, where the outline of the gun can be seen through clothing. For pocket holsters, the external flat side is often the side with a nap, or rougher surface, to hold the holster in place when drawing the pistol.

Sporting holsters cover a wide spectrum of styles: maximum access for Fast Draw shooting, highly adjustable holsters used in IPSC and pin shooting, old-fashioned holsters used in Cowboy Action Shooting, high retention, maximum protection holsters used for handgun hunting, and simple holsters used to hold a handgun while out plinking. Like any sporting equipment, sporting holsters evolve to maximize the benefits given the rules of the game, where applicable, so the competitive sports have the most specialized holsters.

Holsters for hunting can be unique if they are designed to carry large handguns or to make allowances for telescopic sights. Large handguns are often carried in holsters that are slung across the shoulder, and removed from the body before the handgun is drawn. Slow access is acceptable in this case because the handgun is not expected to be used for defensive purposes.

A vertical shoulder holster- the Idaho Leather Company Last Man Standing for the 1911 Colt et al.:

Popular holster types are:

Outside the waistband (OWB) or belt holsters, are most commonly used by police and military, and by citizens who choose to open carry. Belt holsters can be worn high and close to the body, slightly behind the hip bone ("4:00 position"), and can be concealed under a long, untucked shirt or jacket.

Inside the waistband (IWB) holsters, which clip or mount to a belt and allow one to securely holster the weapon inside the pants. Some IWB holsters give the wearer the option of tucking a shirt over the firearm and holster.

Shoulder holsters consist of two straps connected in a manner similar to a backpack, with the actual holster mounted to a strap on the right or the left side. Shoulder holsters are designed to position the handgun: 1. in a vertical position, with the barrel pointed generally toward the ground; 2. in a vertical position, with the barrel pointed generally upward; 3. in a horizontal position, with the barrel pointed generally behind the wearer. Shoulder holsters are typically comfortable for the wearer, as they distribute the weight across the shoulders instead of directly on the belt.

Sling holsters are similar to shoulder holsters, but instead consist of a band worn over one shoulder and another around the chest. This style of holster (designated M3 for the early 1-strap model and M7 for the two-strap model in the U.S. military) was used for pilots, tank operators, and other vehicle drivers in World War II as they were easier to use in the seated position. They became popular with other soldiers who disliked the heavy leather flap on the standard issue M1911-A1 hip holster. They are still produced by the U.S. military for the M9 pistol.

The "belly band" holster is a wide elastic belt with a built-in holster, usually worn under an untucked shirt, to facilitate access. There are various types, worn at the belt line or higher, with the gun placement anywhere from in front to under the armpit. In order to remain in place, a belly band must be extremely tight; this is generally uncomfortable - it is comparable to wearing a girdle.

Small of back holsters place the weapon directly over the center of the back, allowing for even large handguns to be carried with little printing. While both comfortable and stylish, should the wearer fall onto the weapon (such as in a close quarters fight) serious spinal injury may occur. For this reason, in recent times many police departments in the US have disallowed any equipment, gun, handcuffs, etc., to be worn in this position.

Groin holsters place the handgun mostly below the waistline around the 12:00 position. There are few body movement or clothing restrictions with this holster type.

Thigh holsters (also called tactical or drop leg holsters) are a popular military and police item that holds the sidearm on the right leg where the hand naturally hangs, making for a fast draw. Early U.S. cavalry units used these in the early 1900s with a leather thong strapping it to the leg. Modern ones often use a drop leg PALS grid with a modular holster attached, often with buckles for quick release. Police and military personnel wear these when a bulky vest or a full belt (as in the case of K9 officers) makes belt carry impractical.

Ankle (aka "boot") holsters offer excellent concealment and are used by law enforcement officials who wish to carry a secondary weapon to back up their primary firearm. However, many officers find that even a small handgun bounces around too much while running or other physical activity.

Chest holsters can be attached to MOLLE compatible vests and chest carriers. Like shoulder holsters, chest holsters are often easier to draw from than belt holsters when the operator is seated inside a vehicle.

Strut holsters are used exclusively for concealed carry. They are worn above the trouser belt line as a cross draw holster located directly under one’s arm (9 o’clock position) or toward the front of the body (10 to 11 o’clock position). The design contains a strut which is shaped to nest behind one’s trouser belt and attach to the holster at the other end. The strut transfers the weight of the firearm to the belt and retains the weapon in place for secure removal. A flexible band is also attached to the holster and worn above the waist to keep the weapon snug against the body. Concealment is achieved by wearing the unit inside of a shirt which may be tucked in or worn outside.

Pancake holsters are typically made of two pieces of the material with the handgun sandwiched between them, containing at least two belt slots. They should be carried slightly off the hip to the rear part of the back. The pancake style of carry allows pulling the gun tight against the body for a better concealment.

Cross draw belt holsters are designed to be worn outside the waistline, on the weak side of the body (opposite to the dominant hand). Although, the cross-draw carry is often considered to be slower due to the necessary movement across the body; drawing the gun from a seated position can be more comfortable and even quicker carry method comparing to the others. The cross-draw belt holsters may be an ideal option for wearing a backup gun on the waistline and also appropriate choice for women due to the comfort carry and naturally good adaptability to the female body.

Other, specialized types of holsters are designed to be mounted inside briefcases, day planners, purses and filofaxes, or even articles of clothing.

When choosing a holster for a firearm, factors of interest include:

Safety - a well designed holster will provide protection to the handgun during insertion into or removal from the holster or while being carried that will: 1. prevent accidental trigger movement; 2. prevent accidental disengagement of the safety mechanism; 3. prevent forward or rearward movement of the hammer. These features will vary greatly as applicable to the action of the handgun. The safety features of a holster very much require that the holster be engineered and designed for each specific manufacture and model of handgun.

Retention - a holster designed with retention in mind will help prevent a gun from being removed from the holster by anyone other than the person wearing it. Modern duty holsters have multiple hidden retention devices to this end. Frequently, retentive holsters are custom designed for a specific model of gun.

Concealment - it is often desirable not to alert other people of one's being armed. A carefully designed and worn holster can make a gun virtually invisible. Almost all concealment holsters are designed to be worn with a covering garment that is part of the wearer's everyday attire.

Comfort - ability to wear a gun for an extended period without excessive discomfort.

Finish - a well designed holster should not snag a pistol or excessively abrade its finish.

Draw ease - practical shooting holsters allow a gun to be presented quickly, but drawing ease is often compromised in concealed carry

Ease of reholster - a rigid holster will allow a gun to be returned to it with one hand, while a flexible one may collapse after the gun is drawn, requiring the use of both hands to reholster.

Adjustability - a holster that provides for the adjustment of gun cant and position can aid in both comfort or concealment.

Price - modern holsters for a typical standard handgun can cost $20 to $200. Some users will desire multiple holster types per gun, while others prefer a generic holster for carrying multiple gun types.